Systems and methods for detecting a liquid

ABSTRACT

Systems and methods for detecting a liquid. Detection a liquid may include detecting liquid at a boundary of an area and reporting the presence of the liquid. Reporting liquid at a boundary may prevent leaking of the liquid form the area. Detecting also includes detecting liquid inside the area. The amount of liquid detected inside the boundary may relate to a range of amounts of liquid. The minimum amount of the range may represent the minimum amount of liquid that is permissible in the area prior to taking action to deal with the liquid.

FIELD OF THE INVENTION

Embodiments of the present invention relate to systems and methods fordetecting a liquid (e.g., moisture, wetness).

BACKGROUND OF THE INVENTION

Detecting the presence of liquid may include using a system to detectthe liquid. In an application where the system detects liquid in anarea, a user may benefit from a system that detects the exit of theliquid from the area or the presence of a liquid within the area.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the present invention will now be further described withreference to the drawing, wherein like designations denote likeelements, and:

FIG. 1 is a functional block diagram of a system for detecting a liquidaccording to various aspects of the present invention;

FIGS. 2 and 3 are cross-sections of areas that include conductors fordetecting a liquid; and

FIGS. 4-8 are implementations of the conductors of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A system for detecting liquid may include conductors and a determiner. Asystem may detect a liquid (e.g., moisture, wetness). A system maydetect an amount of liquid. A system may detect a physical property, aphysical quantity, and/or a chemical property to detect a liquid. Asystem may detect a change in a physical property, a physical quantity,and/or a chemical property to detect a liquid.

A physical property may include concentration, electric charge,electrical conductivity, electrical impedance, electric potential,inductance, resistivity, and frequency. A chemical property may includePH, composition of the liquid, reactivity, and electromotive force.

A system may detect a liquid in an area. A system may detect whether aliquid is exiting (e.g., leaking, leaving) from an area. The conductorsof a system, or a portion thereof, may be positioned in an area fordetecting a liquid in the area. A portion of the conductors of a systemmay be positioned at or proximate to an outer boundary of an area todetect whether a liquid is exiting the area. An area may include anytwo-dimensional area or three-dimensional volume. An area may be vacantof any material other than air and/or contain a material. A material inan area may absorb a liquid. The conductors of a system, or a portionthereof, may contact (e.g., touch) a material in an area to detect aliquid in the area. A boundary of an area may include an outer edge ofthe area. A boundary may include an outer edge of an absorbent layerpositioned in the area.

A system may provide (e.g., exert, deliver, apply) a force (e.g.,mechanical, electrical, magnetic) to detect a liquid. A system mayprovide a force to an area, or a portion thereof, to detect a liquid inthe area. A system may provide a force to a material in the area todetect a liquid in the material of the area. The force applied by thesystem to an area may cooperate with the physical and/or chemicalproperties of the material and/or a liquid in the area to detect theliquid. A system may measure (e.g., detect), deduce, and/or calculate aphysical property made manifest by application of the force to detect aliquid. A system may detect a physical property of a material in thearea to determine a liquid or absence thereof in the area. A forceapplied by a system to detect a liquid may include an electric force.For example, a system may include conductors that are positioned in anarea. A system may apply a voltage to two or more conductors to detect aliquid.

A material in an area may have an impedance. A magnitude of an impedanceof a material absent a liquid may be different than the magnitude of theimpedance of the material when the material contains (e.g., holds) anamount of liquid. An impedance of a material may be inverselyproportional to an amount of liquid in the material. For example, when amaterial is dry (e.g., absent liquid, not damp) an impedance of thematerial may be high. A high impedance of a material may impede currentflow through the material. Current flow through a material that is drymay be negligible or zero. Low current flow through a material that isdry may be equivalent to an open circuit.

When a material is damp (e.g., wet, contains a liquid), the impedance ofthe material may decrease. The impedance of a material that contains aliquid may be proportional to impedance of the liquid and/or the amountof the liquid in the material. The impedance of a material that containsa liquid may be inversely proportional to an amount of the liquid in thematerial. As the amount of liquid increases per unit volume of thematerial, the impedance of the material may decrease. As the impedanceof a material decreases, a current may flow through the material and/orthe liquid in the material. The flow of a current through the materialand/or liquid in the material may be equivalent to a closed circuit. Anarea in a material that permits the flow of a current may be referred toas an electrical circuit. An electrical circuit, or an area of reducedimpedance, may permit current to flow from one portion of an area toanother portion of the area.

The magnitude of the impedance through a conductive liquid depends onthe distance between electrical probes positioned in the liquid. As thedistance between the probes increases, the amount of liquid between theprobes increases, therefore the impedance between the probes increases.The conductors of conductors 120 perform the function of an electricalprobe in a conductive liquid so that the impedance of the liquid betweenany two conductors is proportional to the distance between theconductors. As used herein, the term “liquid” means a conductive liquid.

Conductors may be positioned proximate to or in a material. Conductorsmay be spaced apart in the material. When the material is substantiallydry, little or no current may flow between the conductors in thematerial. When little or no current flows between conductors via thematerial, an open circuit exits between the conductors. When thematerial is wet, some current may flow between conductors. As the amountof liquid increases in the material, the amount of current that flowsbetween conductors may increase because the impedance between theconductors decreases. When the amount of current that flows betweenconductors reaches a threshold, an electrical circuit (e.g., closedcircuit) exits between the conductors.

A method for detecting a liquid in an area may further provideinformation regarding the extent (e.g., distance, length) of the spreadof the liquid in the area. A system that detects a liquid in a materialhaving known physical properties may further determine an approximatevolume (e.g., amount, quantity) of the liquid in the area.

An area may include a boundary. An outer boundary of an area includes aportion of the area where the area ends. The outer boundary of an areathat includes a material may be the location where the material ends orthe edge of the material. A system may detect liquid at a boundary of anarea. Detecting a liquid at a boundary of an area may be an indication(e.g., evidence, indicia) that the liquid is leaving (e.g., exiting,leaking from) the area.

A user of a system for detecting liquid may assign a differentimportance to detecting liquid at a boundary of an area as opposed todetecting liquid that is within the boundary of the area. For example, asystem may detect liquid in a medical pad that is placed on a patient'sbed. Health care standards may permit a certain amount of liquid to beabsorbed by the pad, but a pad must be immediately changed it liquidleaks from the pad or a leak is imminent. The same standard may apply toa diaper in that it should be immediately change if it starts leaking ormay soon leak. A user may desire a system that provides notice of aminimum amount of liquid within an area and notice when the liquid is ata boundary of the area.

For example, system 100, shown in FIG. 1, may include conductors 120positioned in area 110 and determiner 160. Conductors 120 may includeboundary conductors 130 for detecting a liquid proximate to boundary190. Conductors 120 may include area conductors 140 for detecting aliquid within boundary 190. Conductors 120 may include contacts 150 forfacilitating an electrical, mechanical, and/or physical connection toboundary conductors 130 and/or area conductors 140. Conductors may bepositioned at any location in an area. Conductors may be positioned inand/or on a material in an area. Two examples of conductors positionedin a material in an area are provided in FIGS. 2 and 3. Variousimplementations of conductors (e.g., 400, 500, 600, 700, 800) areprovided in FIGS. 4-8.

Determiner 160 may include processing circuit 162, communication (e.g.,comm) circuit 164, power supply 166, and/or user interface 168. In oneimplementation, determiner 160 includes only processing circuit 162 thatincludes a circuit for determining whether a liquid is present in anarea. A device for receiving information (e.g., reader) from processingcircuit 162 may provide power to processing circuit 162 for performingthe operation of determining whether liquid is present. In anotherimplementation determiner 160 includes processing circuit 162 and powersupply 166. A device for receiving information from processing circuit162 may include a communication circuit for communicating theinformation to other devices.

A conductor may be formed of any material capable of conducting anelectrical current, such as copper, aluminum, gold, silver,semiconductor material, and carbon. A conductor may be formed in anyconventional manner. A conductor may include conductive material in theform of a wire, conductive material deposited onto another material,and/or conductive ink printed on a surface. A conductor may be formed tohave any shape (e.g., width, length) whether uniform or varying. Aconductor may carry (e.g., transport) a current at a voltage. Aconductor may have an impedance. The impedance of the conductor may berelated to the material that forms the conductor, an amount of materialthat forms the conductor, the shape of the conductor, and across-sectional area of the material that forms the conductor. Theconductance of a conductive material formed as a trace (e.g., line) maybe proportional to the number or squares of material that form thetrace.

A power supply includes a supply of energy. Energy may be used forenabling the operation of electronic circuits (e.g., devices) such as aprocessing circuit, a user interface, and/or a communication circuit. Apower supply may include any conventional component for providing energysuch as a battery, a transformer that transforms line power, and/or acapacitor. A power supply may store energy for providing. In the casewhere a determiner is implemented using passive RF technology (e.g.,RFID tag), a power supply may include a coil for transforming (e.g.,converting) transmitted electromagnetic waves from an RF reader intoelectrical energy. Energy from a power supply may be used as a force fordetecting a liquid as discussed above.

A communication (e.g., comm) circuit may provide (e.g., transmit) and/orreceive information (e.g., data). A communication circuit may transmitand/or receive (e.g., communicate) information via a wireless linkand/or a wired connection. A communication circuit may communicate usingany conventional protocol for wireless (e.g., radio, light, sound,vibrations) and/or wired (e.g., electrical, optical) mediums. Acommunication circuit may receive information from a processing circuitfor transmission. A communication circuit may provide receivedinformation to a processing circuit.

A user interface may include electronic devices (e.g., switches, pushbuttons, touch screen, Bluetooth transceiver) for receiving information(e.g., data) from a user. A user may manually manipulate one or moreelectronic devices of a user interface to provide information.Electronic devices for receiving information from a user may include awireless receiver that receives information from an electronic device(e.g., smart phone, tablet, watch, pager). A user may manually provideinformation to a user interface via a electronic device. A userinterface may include electronic devices for providing information to auser. A user may receive visual and/or auditory information from a userinterface. A user may receive visual information via devices (e.g., LCDscreen, LEDs) that display information. A user interface may include awireless transmitter for transmitting information to an electronicdevice for presentation to a user.

A user interface may receive information for providing to a user from aprocessing circuit, a communication circuit, and/or a power supply.Information may include status of the power supply, informationcommunicated via the communication circuit, notice of detected liquid,and location of detected liquid. Information received by a userinterface from a user may be provided to a power supply, a processingcircuit, and/or a communication circuit. Information from a user mayinstructions (e.g., information) for controlling an operation of thedeterminer. Information from a user may include communication parametersfor a communication circuit, information regarding an area, informationregarding a material in an area, an amount of force (e.g., voltage) toapply to detect a liquid, a frequency of applying a force to detect aliquid, and an instruction to reset operations. Information from a usermay be used by a processing circuit to control the operation of a systemfor detecting liquid.

A communication circuit in combination with an electronic device (e.g.,smart phone, tablet) may perform the functions of a user interface sothat user interface 168 may be omitted.

A processing circuit includes any conventional circuit. A processingcircuit may include passive electronic devices (e.g., resistors,capacitors, inductors) and/or active electronic devices (op amps,comparator, analog-to-digital converter, digital-to-analog converter,microprocessors, programmable logic, semi-conductor memory). Aprocessing circuit includes any conventional circuit that providesand/or receives an electrical signal whether digital and/or analog innature. A processing circuit may include conventional data buses,analog-to-digital converters, output ports, input ports, timers, logiccircuits, memory, and arithmetic units. A processing circuit may includeany conventional microcontroller, microprocessor, signal processor,logic circuits, and/or programmable logic. A processing circuit maystore information (e.g., data). A processing circuit may manipulatedata.

A processing circuit may apply a force to detect a liquid. A processingcircuit may detect a physical property and/or a change in a physicalproperty to detect a liquid. A processing circuit may provide a currentand/or voltage (e.g., signal) via an output port to detect a liquid. Aprocessing circuit may provide a signal in accordance with an interval.A processing circuit may detect a signal via an input port to detect aphysical property and/or a change in a physical property. A processingcircuit may measure a characteristic (e.g., magnitude, duration) of asignal via an input port. A processing circuit may apply a force, detect(e.g., measure) a physical characteristic, and perform a calculationusing the detected physical characteristics.

A processing circuit may store measured (e.g., detected) data, performcalculations using measured data whether presently detected orpreviously detected and stored, transform detected data from one form toanother, and provide a notice responsive to a result of an operation.

An input and/or output port of a processing circuit may electricallycouple to one or more conductor of conductors 120. A processing circuitmay apply a force to conductors 120. A processing circuit may measure aresponse of conductors 120 to a force applied to conductors 120. Aprocessing circuit may store information regarding the characteristicsof the conductors of conductors 120. A processing circuit may use storedinformation regarding the characteristics of the conductors ofconductors 120 to detect a liquid in an area. A processing circuit mayapply a force to selected conductors of conductors 120. A processingcircuit may use information measured from conductors 120 to perform anoperation. Operations responsive to information measured from conductors120 may include further and/or different measurements, application of anadditional force, and providing a notice.

In an implementation, determiner 160 includes a conventionalmicrocontroller with input and output ports and at least one data busfor communicating with communication circuit 164. Processing circuit 162electrically couples to boundary conductors 130 and/or area conductors140 via contacts 150. Power supply 166 includes a conventional battery.

In area 200 of FIG. 2, processing circuit 162 electrically couples toboundary conductors 222 and 224. In area 300 of FIG. 3, processingcircuit 162 electrically couples to area conductors 322 and 324.Conductors 222 and 224 and/or conductors 322 and 324 may be implementedas conductive traces printed onto absorbent layer 210. Conductors 222and 224 are positioned proximate to boundary 290 of area 200 which isproximate to the edge of absorbent layer 210 and/or substrate 240.Conductors 322 and 324 are not proximate to boundary 290 or any otherboundary of area 300, but are positioned within area 300 away theboundary.

Conductors in an area may be positioned above an absorbent layer and/orbelow an absorbent layer. Boundary conductors 130 and/or area conductors140 may be positioned above and/or below an absorbent layer. Boundaryconductors 130 may be positioned on a same side and/or different sidesof an absorbent layer. Area conductors 140 may be positioned on a sameside and/or different sides of an absorbent layer. Boundary conductors130 may be positioned on a same side and/or a different side of anabsorbent layer as area conductors 140.

Substrate 240 is formed of a non-permeable (e.g., non-absorbent)material that is positioned proximate a surface and/or object that is tobe protected from the liquid. A surface may include any surface (e.g.,wood, metal, tile). An object may include any object (e.g., furniture,electronic devices). Substrate 240 stops the movement of liquid fromabsorbent layer 210 to the surface and/or object. Substrate 240 isformed of a material that is an electrical insulator so that a circuitcannot form between conductors 222 and 224 or conductors 322 and 324through substrate 240. Conductors may be positioned (e.g., printed) on asubstrate. Absent an absorbent layer, liquid may spread across asubstrate to establish an electrical circuit between conductors on thesubstrate.

A substrate need not be limited to a planar (e.g., flat) contour. Asubstrate may have edges near a boundary of the substrate that areelevated above the area (e.g., center) of the substrate so that a liquidmay accumulate in the lower elevations of the substrate before overflowing. Absent an absorbent layer, area conductors 140 on the substratemay detect a liquid when only a small amount of liquid is on thesubstrate. As the liquid accumulates on the substrate the level of theliquid may rise until it establishes an electrical circuit betweenboundary conductors 130 near the boundary of the substrate.

A substrate may be formed of two or more layers of the same and/ordifferent materials.

To detect liquid, processing circuit 162 applies a voltage (e.g., force)to conductors 222 and 224 or conductors 322 and 324 and measures acurrent and/or a voltage that results from the application of thevoltage. Absorbent layer 210 is formed of a material with a lowconductivity (e.g., high impedance) when dry so that little or nocurrent flows between conductor 222 and 224 or conductors 322 and 324when absorbent layer 210 contains little or no liquid. Because little orno current flows between conductors 222 and 224 or conductors 322 and324 when absorbent layer 210 contains little or no liquid, processingcircuit 162 cannot detect an electrical circuit (e.g., open circuit)between conductors 222 and 224 or conductors 322 and 324.

When liquid 250 or 350 is present in absorbent layer 210, the impedanceof absorbent layer 210 is reduced from a very high impedance, possiblyclose to infinite (e.g., open circuit), to a lower impedance thatpermits a current to flow between conductors 222 and 224 or conductors322 and 324 via liquid 250 or 250 respectively. Processing circuit 162may detect a threshold current and/or voltage between conductors todetermine whether an electrical circuit exists between conductors. Ifthe magnitude of the current between conductors is greater than athreshold or the magnitude of the voltage drop between conductors isless than a threshold, processing circuit 162 may determine that anelectrical circuit exists between conductors.

An electrical circuit may develop between two conductors due to areduced magnitude of the impedance between conductors. The impedance maybe reduced by introducing a liquid having a low impedance and/or a highconductivity into the material. For example, the impedance of urineranges from 10 ohms to 100 ohms per unit volume. The impedance of bloodranges from 300 to 550 ohms per unit volume. The impedance of liquidssuch as urine and/or blood is inversely proportional to the amount ofsalts in the liquid. The liquid in the absorbent material acts todecrease the impedance of the material in the area of the liquid. Areduced magnitude of impedance in an area between conductors permits acurrent to flow between the conductors. A threshold current flowingand/or voltage between conductors may be used to specify that a circuitexists between the conductors.

Processing circuit 162 may determine that an electrical circuit exitsbetween conductors whenever a current or a voltage travels between twoconductors without calculating a magnitude of an impedance between theconductors. In another implementation, processing circuit 162 maydetermine the magnitude of the impedance between conductors in order todetermine the chemical composition of the liquid (e.g., urine, blood) inthe area. A processing circuit may use information that relatesimpedance to chemical composition to provide a notice of detected liquidthat includes information as to the possible composition of the liquid.Impedance information that relates impedance to chemical composition maybe further related to the material that forms absorbent layer 210 andany possible interaction the liquid may have with the absorbent layer.

Upon detecting an electrical circuit and/or impedance below a threshold(e.g., reduced impedance) between two conductors (e.g., 222/224,322/324), processing circuit 162 performs a function related todetecting a liquid. When processing circuit 162 detects an electricalcircuit between conductor 222 and conductor 224, processing circuit 162performs a function of reporting that a liquid had been detected.Processing circuit 162 may further report that the liquid is proximateto a boundary, in this case boundary 290, or crossing a boundary of area200. When processing circuit 162 detects an electrical circuit betweenconductor 322 and conductor 324, processing circuit 162 performs afunction of reporting that a liquid has been detected. Processingcircuit 162 may further report that the liquid is not proximate to aboundary, but that is located (e.g., positioned) within area 300. Thenotices may be communicated to a user via communication circuit 164, viaan audible indicator of user interface 168, and/or via a visualindicator of user interface 168.

In accordance with a distance between two conductors, processing circuit162 may determine a spread and possibly a minimum volume of the liquidin an area. Conductors may have a spacing between each other that isknown or detectable to processing circuit 162. The existence of acircuit between two conductors indicates that a liquid has spreadbetween the two conductors. A processing circuit that has informationregarding the spacing of conductors may determine the spread of theliquid due to the existence of a circuit. A liquid may have a knownimpedance per unit area or unit volume. A processing circuit maydetermine the impedance through a liquid and use information regardingthe impedance of the liquid to determine the spread and/or concentrationof the liquid.

For example, upon detecting a circuit between conductors 222 and 224,processing circuit 162 may use stored information to determine that thespacing between conductors 222 and 224 is a distance 270. Processingcircuit 162 may use stored information to determine that the distancebetween conductors 322 and 324 is distance 370. Knowing the distancebetween two conductors that have an electrical circuit between eachother provides processing circuit 162 the information that the liquidhas spread at least the distance that separates the conductors. Assuminguniform absorption of the liquid in the absorbent material, the distancebetween conductors infers an area of liquid spread. Accordingly,detecting an electrical circuit provides information as to a minimumarea that the liquid had spread. For example, the area that a liquid hasspread may be inferred by assuming a substantially circular spread ofthe liquid, so that the area of the spread between conductors 222 and224 is the area of the circle represented by radius R252. The area ofthe spread between conductors 322 and 324 is the circular arearepresented by radius R352.

Information regarding the absorptive characteristics of the absorbentlayer may be used to infer a volume from the area of spread of theliquid. At a minimum, the thickness 260 of absorbent layer 210 may beused with the area of spread to calculate a possible volume of detectedliquid. Processor 162 may further have information as to any change inthickness of absorbent layer 210 as it absorbs liquid to aid indetermining a possible volume of detected liquid.

An absorbent layer may be formed of one or more layers of the samematerial and/or different materials. For example, an absorbent layer maybe formed of a highly absorbent material and a material that wicksmoisture away from an object placed on the absorbent layer. The layerthat wicks moisture transfers moisture from the object into the highlyabsorbent material to be absorbed. A layer that wicks moisture mayinclude a material that enables the passage of liquid in a singledirection. For example, a wicking layer may permit passage of liquid toan absorbent layer, but inhibit movement of the liquid out of theabsorbent layer. An object that may be placed on top of an absorbentlayer may include a human or animal.

The magnitude of the impedance between two conductors may providefurther information as to the volume of a liquid between two conductors.Impedance R226 represents a reduced impedance between conductors 222 and224 due to the presence of liquid 250. As discussed above a thresholdvalue of the magnitude of impedance R226 may be used to indicate that anelectrical circuit exists between conductors 222 and 224. Rather thandetermining only that impedance R226 is less than a threshold,processing circuit 162 may perform measurements to determine a value ofthe magnitude of the impedance of R226. Processing circuit 162 may usethe value of the magnitude of impedance R226 to determine whetherabsorbent layer 210 is lightly damp, moderately damp, and/or saturated.Processing circuit 162 may use the value of the impedance to infervarying and/or increasing minimum volumes of liquid between conductors222 and 224.

The same type of measurements and inference may be used to determine aminimum volume of liquid 360 between conductors 322 and 324 inaccordance with the magnitude of impedance R336, distance 370, andthickness 360 of absorbent layer 210.

Although boundary 290 is drawn to the left, referring to FIG. 2, ofconductors 222 and 224, boundary 290 may be drawn between conductors 222and 224 or even to the right of conductor 222. Two conductors proximateto a boundary may detect liquid at the boundary. Two conductors may bepositioned with respect to a boundary of an area to detect when a liquidmay exit the area. Liquid crossing a boundary and/or exiting an area mayresult in undesirable consequences. An electric circuit between theconductors positioned proximate to a boundary indicates that a liquid isbetween the conductors and at the boundary. Depending on the position ofthe boundary with the edge of the area, liquid at the boundary mayindicate that a leak is imminent.

In accordance with system for detecting liquid discussed above,conductors may be placed in an area to detect a liquid in the area awayfrom a boundary and detect a liquid at a boundary. Using informationrelated to conductor spacing, conductor location, characteristics of theabsorbent material, and characteristics of liquids that may be present,a processing circuit may infer an area of spread of a liquid, a volumeof a liquid, a chemical composition of a liquid, and/or a magnitude ofsaturation of an absorbent layer. Implementations 400, 500, 600, 700,and 800 of conductors 120 are discussed below.

Implementations 400 and 500 include conductor 470, conductor 480, andconductor 490. Conductor 490 is positioned along boundary 410 tosurround (e.g., encircle, encompass) boundary 410. Portions ofconductors 470 and 480 are positioned along boundary 410 so that twoconductors (e.g., conductor 490, portions of conductors 470 and 480) arepositioned along the boundary. Along the boundary, conductors 470, 480,and/or 490 are positioned distance 450 away from each other. In oneimplementation, conductors 470, 480, and/or 490 are positioned at mostdistance 450 away from each other along boundary 410. Distance 450 mayrelate to the absorbency of an absorbent layer in area 430. Distance 450may be proportional to the absorbency of the absorbent layer in thearea. Distance 450 may be greater for absorbent layers that are highlyabsorbent where liquid moves less quickly beyond the boundary to createa leak. Distance 450 may be less for absorbent layers that are lessabsorbent where a liquid may spread more rapidly past boundary 410 toexit area 438 to leak. Although the distance between conductors 470,480, and/or 490 is shown as distance 450 along the entire boundary 410,the distance between conductors 470, 480, and/or 490 may be differentalong one or more portions of boundary 410.

The volume of a liquid detected along boundary 410 may include a rangeof volumes of liquid. The volume of a liquid along boundary 410 is inaccordance with the range of spread and the absorbent characteristics ofthe material along boundary 410. A highly absorbent material may resultin a larger volume of liquid along boundary 410 before it is detectedthan a less absorbent material.

The distance between conductors 470 and 480 within boundary 410 isdistance 460. In one implementation, the distance between conductors 470and 480 within boundary 410 is at least (i.e., no less than) distance460. Distance 460 may be greater than distance 450 because a liquid mayspread farther inside boundary 410 than outside of boundary 410 withoutresulting in a leak. Inside the boundary, distance 460 betweenconductors 470 and 480 permits a liquid to spread within a range beforethe liquid is detected. The volume of a liquid detected inside boundary410 may include a range of volumes of liquid. The volume of a liquidinside boundary 410 is in accordance with the range of spread and theabsorbent characteristics of the material within boundary 410. A highlyabsorbent material may result in a larger volume of liquid insideboundary 610 before it is detected than a less absorbent material.

Because distance 460 is greater than distance 450, the volume of liquidwithin boundary 410 is greater than the volume of liquid along boundary410 before the liquid is detected assuming that the absorbent layeralong boundary 410 is similar to the absorbent material within boundary410.

To detect a liquid, processing circuit 162 applies a voltage betweenconductors 470, 480, and/or 490 to determine whether an electricalcircuit exits. As discussed above, when little or no liquid is present,the impedance between conductors 470, 480, and/or 490 is very high orpossibly infinite. As liquid spreads between conductors 470, 480, and/or490, whether or not an absorbent layer is present, the impedance betweenconductors 470, 480, and/or 490 decreases. When the magnitude of theimpedance between any two conductors is at or below a threshold, anelectrical circuit between the conductors exists.

The three conductors and their placement as shown in implementations400, 500, and 600 enables determiner 160 to distinguish between liquidpositioned at boundary 410 and liquid positioned within boundary 410 bytesting for the existence of an electrical circuit between conductors.In implementation 400, an electrical circuit between conductors 490 and470 or conductors 490 and 480 indicates that there is liquid alongboundary 410, but not necessarily inside boundary 410. An electricalcircuit between conductor 470 and 480 indicates that there is liquidinside boundary 410, but not necessarily along boundary 410. Anelectrical circuit between conductors 490 and 470 or conductors 490 and480 and no circuit between conductors 470 and 480 indicates that liquidis at boundary 410, but not within boundary 410. An electrical circuitbetween conductors 470 and 480 and no circuit between conductor 490 andconductor 470 or conductor 480 indicates liquid within boundary 410, butno liquid at boundary 410.

With respect to implementation 500, an electrical circuit betweenconductors 490 and 480 indicates liquid along boundary 410, but notwithin boundary 410. An electrical circuit between conductors 470 and480 indicates liquid within boundary 410.

Within boundary 410, the range of the spread of the liquid before theliquid may be detected is represented by the diameter of liquids 430 and434. Depending on where the liquid is introduced in the area (e.g., 432,436), a liquid may spread a distance of 460 (e.g., liquid 430) beforethe liquid spreads between conductors 470 and 480 thereby permittingdeterminer 160 to detect the liquid. Liquid introduced at location 436may spread up to a distance of about two times distance 460 (e.g.,liquid 434) before the liquid contacts conductors 470 and 480 therebycreating a circuit.

As discussed with respect to FIGS. 2 and 3, an area of spread may relateto a volume of liquid in an absorbent layer, so a range of spread of aliquid, as discussed above, may relate to a range of volumes of liquidin an absorbent layer.

At the boundary, the range of the spread of liquid is represented by thediameter of liquid 440 and 444. Depending on where the liquid isintroduced (e.g., 442, 446) with respect to the boundary, a liquid mayspread a distance of 450 (e.g., liquid 440) before the liquid spreadsbetween conductors 470 and 480 or a distance less than distance 460(e.g., liquid 444) before the liquid contacts conductors 470 and 480thereby creating a circuit at the boundary.

The amount of spread of a liquid before the liquid may be detected,whether at a boundary or within a boundary, is in accordance with thedistance between the conductors in the area. When a liquid spreadsbetween two conductors, the liquid establishes a circuit between theconductors. Detecting the circuit, or an impedance less than athreshold, indicates the presence of the liquid. The distance betweenthe conductors determines how much liquid may be absorbed by anabsorbent layer before the liquid is detected. The amount (e.g., spread,volume) of liquid present is proportional to the distance between theconductors. As discussed above, with knowledge of the absorbent layer,it is possible to estimate a volume of liquid between the conductorswhen liquid is detected.

Upon detecting a circuit, processing circuit 162 may provide a notice.For implementations 400, processing circuit 162, upon detecting anelectrical circuit between conductor 490 and 470 or 490 and 480, mayprovide a notice that liquid is at boundary 410. Upon detecting anelectrical circuit between conductors 470 and 480, processing circuit162 may provide a notice that liquid is located within boundary 410.

For implementation 500, processing circuit 162, upon detecting anelectrical circuit between conductors 490 and 480 may provide a noticethat liquid is at boundary 410. Upon detecting an electrical circuitbetween conductors 470 and 480, processing circuit 162 may provide anotice that liquid is located within boundary 410.

Conductors 470 and 480 may include contacts 472 and 482 respectively tofacilitate mechanical and/or electrical coupling of determiner 160 toconductors 470 and 480. Contacts 472 and 482 may also couple to an RFcircuit (e.g., RFID tag) and determiner 160 may include an RF reader.

Implementation 600 also includes conductor 670, conductor 680, andconductor 690. Portions of conductors 670, 680, and 690 are positionedalong boundary 610. Conductor 690 separates area 638 into two regions(e.g., zones) and also surrounds boundary 610. Along boundary 610,conductors 690, 670, and/or 680 are positioned distance 650 away fromeach other. In one implementation, conductors 690, 670, and/or 680 arepositioned at most distance 650 away from each other along boundary 610.As discussed above with respect to conductor 450, distance 650 mayrelate to the absorbency of an absorbent layer in area 638. Furtherdistance 650 may be different along one or more portions of boundary610.

The volume of a liquid detected along boundary 610 may include a rangeof volumes of liquid. The volume of a liquid along boundary 610 is inaccordance with the range of spread and the absorbent characteristics ofthe material along boundary 610. A highly absorbent material may resultin a larger volume of liquid along boundary 610 before it is detectedthan a less absorbent material.

The distance between conductors 670 and 680 within boundary 610 isdistance 660. In one implementation, the distance between conductors 670and 680 within boundary 610 is at least (i.e., no less than) distance660. Distance 660 may be greater than distance 650 because a liquid mayspread farther inside boundary 610 than outside of boundary 610 withoutresulting in a leak. Inside the boundary, distance 660 betweenconductors 670 and 680 permits a liquid to spread within a range beforethe liquid is detected. The volume of a liquid detected inside boundary610 may include a range of volumes of liquid. The volume of a liquidinside boundary 610 is in accordance with the range of spread and theabsorbent characteristics of the material within boundary 610. A highlyabsorbent material may result in a larger volume of liquid insideboundary 610 before it is detected than a less absorbent material.

Because distance 660 is greater than distance 650, the volume of liquidwithin boundary 610 is greater than the volume of liquid along boundary610 before the liquid is detected assuming that the absorbent layeralong boundary 610 is similar to the absorbent material within boundary610.

To detect a liquid, processing circuit 162 applies a voltage betweenconductors 670, 680, and/or 690 to determine whether an electricalcircuit exits. As discussed above, when little or no liquid is present,the impedance between conductors 670, 680, and/or 690 is very high orpossibly infinite. As liquid spreads between conductors 670, 680, and/or690, whether or not an absorbent layer is present, the impedance betweenconductors 670, 680, and/or 690 decreases. When the magnitude of theimpedance between any two conductors is at or below a threshold, anelectrical circuit between the conductors exists.

The conductors as laid out in implementation 600 do not permitdeterminer 160 to distinguish between liquid positioned at boundary 610and liquid positioned within boundary 610 by testing for the existenceof an electrical circuit, but determiner 160 may determine whetherliquid is positioned in region 610 or region 620.

In implementation 600, an electrical circuit between conductors 690 and670 indicates the presence of liquid within region 610 either atboundary 610 or within boundary 610. An electrical circuit betweenconductors 690 and 680 indicates the presence of liquid within region620 either at boundary 610 or within boundary 610.

In an implementation where area 638 is implemented as a pad for ahospital bed, a nurse would want to change the pad if liquid at boundary610 is about to leak or if the pad holds a minimum volume of liquidrepresented by liquid 630 or 634. The nurse would not need to receive anotice of liquid that distinguishes between liquid at boundary 610 are aminimum amount of liquid within boundary 610 because in either case, thepad must be changed.

Within boundary 610, the range of the spread of the liquid before theliquid may be detected is represented by the diameter of liquids 630 and634. Depending on where the liquid is introduced in the area (e.g., 632,636), a liquid may spread a distance of 660 (e.g., liquid 630) beforethe liquid spreads between conductors 670 and 680 thereby permittingdeterminer 160 to detect the liquid. Liquid introduced at location 636may spread up to a distance of about two times distance 660 (e.g.,liquid 634) before the liquid contacts conductors 670 and 680 therebycreating a circuit.

As discussed with respect to FIGS. 2 and 3, an area of spread may relateto a volume of liquid in an absorbent layer, so a range of spread of aliquid, as discussed above, may relate to a range of volumes of liquidin an absorbent layer.

At the boundary, the range of the spread of liquid is represented by thediameter of liquid 640 and 644. Depending on where the liquid isintroduced (e.g., 642, 646) with respect to the boundary, a liquid mayspread a distance of 650 (e.g., liquid 640) before the liquid spreadsbetween conductors 670 and 680 or a distance less than distance 660(e.g., liquid 644) before the liquid contacts conductors 670 and 680thereby creating a circuit at the boundary.

As discussed above, the amount of spread of a liquid before the liquidmay be detected is in accordance with the distance between theconductors in the area. The volume of the liquid between conductors isproportional to the distance between the conductors.

Upon detecting a circuit, processing circuit 162 may provide a notice.For implementations 600, processing circuit 162, upon detecting anelectrical circuit between conductor 690 and 670 may provide a noticethat liquid is within region 610 either at boundary 610 or in withinboundary 610. Upon detecting an electrical circuit between conductor 690and 680, processing circuit 162 may provide a notice that liquid iswithin region 620 either at boundary 610 or in within boundary 610.

Conductors 670, 680, and 690 may include contacts 672, 682, and 692respectively to facilitate mechanical and/or electrical coupling ofdeterminer 160 to conductors 670, 680, and 690. Contacts 672, 682, and692 may also couple to an RF circuit (e.g., RFID tag) and determiner 160may include an RF reader.

Implementation 700 includes conductors 770, 780, 790, and 796. Conductor790 along with portions of conductors 770 and 780 are positioned alongthe boundary 710 of area 738. Along boundary 710, conductors 790 and 770or 780 are positioned a distance 750 away from each other. In oneimplementation, conductors 790 and 770 or 780 are positioned at most adistance 750 away from each other along boundary 710. As discussed abovewith respect to distance 450, distance 750 may relate to the absorbencyof an absorbent layer in area 738. Further distance 750 may be differentalong one or more portions of boundary 710.

The volume of a liquid detected along boundary 710 may include a rangeof volumes of liquid. The volume of a liquid along boundary 710 is inaccordance with the range of spread and the absorbent characteristics ofthe material along boundary 710. A highly absorbent material may resultin a larger volume of liquid along boundary 710 before it is detectedthan a less absorbent material.

The distance between conductor 796 and conductors 770 or 780 withinboundary 710 is distance 760. In one implementation, the distancebetween conductor 796 and conductors 770 or 780 within boundary 710 isat least (i.e., no less than) distance 760. As discussed above withrespect to conductors 470 and 480, distance 760 may be greater thandistance 750. The volume of a liquid detected inside boundary 710 mayinclude a range of volumes of liquid. The volume of a liquid insideboundary 710 is in accordance with the range of spread and the absorbentcharacteristics of the material within boundary 710. A highly absorbentmaterial may result in a larger volume of liquid inside boundary 710before it is detected than a less absorbent material.

Because distance 760 is greater than distance 750, the volume of liquidwithin boundary 710 is greater than the volume of liquid along boundary710 before the liquid is detected assuming that the absorbent layeralong boundary 710 is similar to the absorbent material within boundary710.

To detect a liquid, processing circuit 162 applies a voltage betweenconductors 770, 780, 790, and/or 796 to determine whether an electricalcircuit exits between any of the conductors. As discussed above, whenlittle or no liquid is present, the impedance between conductors 770,780, 790, and/or 796 is very high or possibly infinite. As a liquidspreads between conductors 770, 780, 790, and/or 796, whether or not anabsorbent layer is present, the impedance between conductors 770, 780,790, and/or 796. When the magnitude of the impedance is at or below athreshold, an electrical circuit between conductors 770, 780, 790,and/or 796.

Within boundary 710, the range of the spread of the liquid isrepresented by the diameter of liquids 730 and 734. Depending on wherethe liquid is introduced in the area (e.g., 732, 736), a liquid mayspread a distance of 760 (e.g., liquid 730) before the liquid spreadsbetween conductor 796 and conductors 770 or 780 or up to a distance ofabout two times distance 760 (e.g., liquid 734) before the liquidcontacts conductor 796 and conductor 770 or 780 thereby creating acircuit.

As discussed with respect to FIGS. 2 and 3, an area of spread may relateto a volume of liquid in an absorbent layer, so a range of spread of aliquid, as discussed above, may relate to a range of volumes of liquidin an absorbent layer.

At boundary 710, the range of the spread of liquid is represented by thediameter of liquid 740 and 742. Depending on where the liquid isintroduced with respect to boundary 710 (e.g., 742, 746), a liquid mayspread a distance 750 (e.g., liquid 740) before the liquid spreads fromconductor 770 or 780 to conductor 790 or less than distance 760 (e.g.,liquid 744) before the liquid contacts conductor 790 and either 770 or780 thereby creating a circuit at boundary 710.

The existence of an electrical circuit between conductor 790 andconductor 770 or conductor 790 and conductor 780 indicates that there isa liquid along boundary 710. An electric circuit between conductors 790and 770 or conductors 790 and 780 does not provide information as towhether liquid is inside the boundary. An electrical circuit betweenconductors 790 and 770 indicates that the liquid is along boundary 710in region 720. An electrical circuit between conductors 790 and 780indicates that the liquid is along boundary 710 in region 722.

The existence of an electrical circuit between conductor 770 and 796indicates liquid within boundary 710 and within region 720. Anelectrical circuit between conductor 780 and 796 indicates a liquidwithin boundary 710 and within region 722. An electrical circuit betweenconductor 796 and both conductors 770 and 780 indicates a liquid withinboundary 710 and within regions 720 and 722.

Upon detecting an electrical circuit between conductors 790 and 770 orconductors 790 and 780, processing circuit 162 may provide a notice thatliquid is at boundary 710. If the circuit is detected between conductor770 and 790 or conductors 790 and 780, processing circuit 162 mayprovide further information that the location of the liquid at boundary710 is in region 720 or 722 respectively. Upon detecting an electricalcircuit between conductors 770 and 796 or conductors 780 and 796,processing circuit 162 may provide a notice that liquid is withinboundary 710 and within region 720 or region 722 respectively.

Conductors 770, 780, 790, and 796 may include contacts 772, 782, 792,and 798 to facilitate mechanical and/or electrical coupling ofdeterminer 160 to conductors 770, 780, 790, and 796. Contacts 772, 782,792, and 798 may also couple to an RF circuit (e.g., RFID tag) anddeterminer 160 may include an RF reader.

Implementation 800 includes conductors 870, 880, 882, and 890. Conductor890 and portions of conductor 870 are positioned along boundary 802 ofarea 826. Along boundary 802, conductors 890 and 870 are positioneddistance 850 away from each other. In one implementation, conductors 890and 870 are positioned at most distance 850 away from each other alongboundary 802. As discussed above with respect to distance 450, distance850 may relate to the absorbency of an absorbent layer in area 826.Although the distance between conductors 890 and 870 is shown asdistance 850 along boundary 802, the distance between conductors 890 and870 may be different along one or more portions of boundary 802.

The volume of a liquid detected along boundary 810 may include a rangeof volumes of liquid. The volume of a liquid along boundary 810 is inaccordance with the range of spread and the absorbent characteristics ofthe material along boundary 810. A highly absorbent material may resultin a larger volume of liquid along boundary 810 before it is detectedthan a less absorbent material.

The distance between conductors 870, 880, and 882 within boundary 802 isdistance 860. In one implementation, the distance between conductors870, 880, and 882 within boundary 802 is at least (i.e., no less than)distance 860. As discussed above with respect to conductors 470 and 480,distance 860 may be greater than distance 850. The volume of a liquiddetected inside boundary 810 may include a range of volumes of liquid.The volume of a liquid inside boundary 810 is in accordance with therange of spread and the absorbent characteristics of the material withinboundary 810. A highly absorbent material may result in a larger volumeof liquid inside boundary 810 before it is detected than a lessabsorbent material.

Because distance 860 is greater than distance 850, the volume of liquidwithin boundary 810 is greater than the volume of liquid along boundary810 before the liquid is detected assuming that the absorbent layeralong boundary 810 is similar to the absorbent material within boundary810.

To detect a liquid, processing circuit 162 applies a voltage betweenconductors 870, 880, 882, and/or 890 to determine whether an electricalcircuit exits between any of the conductors. As discussed above, whenlittle or no liquid is present, the impedance between conductors 870,880, 882, and/or 890 is very high or possibly infinite. As a liquidspreads between conductors 870, 880, 882, and/or 890, whether or not anabsorbent layer is present, the impedance between conductors 870, 880,882, and/or 890 decreases. When the magnitude of the impedance is at orbelow a threshold, an electrical circuit between conductors 870, 880,882, and/or 890 exists.

Within boundary 802, the range of the spread of the liquid isrepresented by the diameter of liquids 830 and 834. Depending on wherethe liquid is introduced in the area (e.g., 832, 836), a liquid mayspread a distance of 860 (e.g., liquid 830) before the liquid spreadsbetween conductors 870 and 880 or conductors 882 and 870 or up to adistance of about two times distance 860 (e.g., liquid 834) before theliquid contacts conductors 870 and 880 or conductors 882 and 870 therebycreating a circuit.

As discussed with respect to FIGS. 2 and 3, an area of spread may relateto a volume of liquid in an absorbent layer, so a range of spread of aliquid, as discussed above, may relate to a range of volumes of liquidin an absorbent layer.

At boundary 802, the range of the spread of liquid is represented by thediameter of liquid 840 and 842. Depending on where the liquid isintroduced (e.g., 842, 846) with respect to the boundary, a liquid mayspread a distance 850 (e.g., liquid 840) before the liquid spreadsbetween conductors 870 and 890 or less than distance 860 (e.g., liquid844) before the liquid contacts conductor 890 and 870 thereby creating acircuit at boundary 802.

Between the conductors 880 and 882, the range of the spread of liquid isrepresented by the diameter of liquid 812 and 816. Depending on wherethe liquid is introduced with respect to regions 820 and 822 (e.g., 814,818), a liquid may spread a distance 810 (e.g., liquid 812) before theliquid spreads between conductor 880 and conductor 882 or more thandistance 810 (e.g., liquid 816) before the liquid contacts conductors880 and 882 thereby creating a circuit.

The existence of an electrical circuit between conductor 890 andconductor 870 indicates that there is a liquid along boundary 802. Anelectric circuit between conductors 890 and 870 does not provideinformation as to whether liquid is inside boundary 802. An electricalcircuit between conductors 890 and 870 indicates that the liquid isalong boundary 802 in region 820, 822, and/or 828.

The existence of an electrical circuit between conductor 870 and 880indicates liquid within boundary 802 and within region 820. Anelectrical circuit between conductor 882 and 870 indicates a liquidwithin boundary 802 and within region 822. The existence of anelectrical circuit between conductor 880 and conductor 882 indicatesthat there is liquid in region 828.

Upon detecting an electrical circuit between conductors 890 and 870,processing circuit 162 may provide a notice that liquid is at boundary802. Upon detecting an electrical circuit between conductors 870 and880, conductors 880 and 882, or conductors 882 and 890, processingcircuit 162 may provide a notice that liquid is within boundary 802 andwithin region 820, region 828, or region 822 respectively.

Conductors 870, 880, 882, and 890 may include contacts 872, 884, 886,and 892 to facilitate mechanical and electrical coupling of determiner160 to conductors 870, 880, 882, and 890. Contacts 872, 884, 886, and892 may also couple to an RF circuit (e.g., RFID tag) and determiner 160may include an RF reader.

Implementation of a Pad for a Hospital Bed

Prolonged exposer to urine and other liquids is one of the primarycauses for bedsores, rashes, and other skin irritation for patients. Thecost and labor associated with the treatment of bedsores and other skinconditions is a major issue for hospitals and long-term medical carefacilities. The total cost of incontinence care products is less than 2%of a hospital or long-term care facilities operating cost. However, thelabor cost associated with incontinence care and the treatment ofbedsores and other related skin conditions can exceed 15% of totaloperating expenses.

Advanced incontinence pads have been designed to wick moisture andliquids away from the patient and capture the liquid in one or moreabsorbent layers of material. The goal is to keep the patient as dry aspossible. Hospital incontinence pads are typically composed of threelayers; a non-permeable bottom layer, an absorbent middle layer, andpermeable top layer. The permeable top layer top is designed to promotethe movement of liquid and moisture away from the patient. The highlyabsorbent middle layer then retains the liquid.

Advanced incontinence pads from manufacturers such as Covidien, Attends,Tranquility and other manufactures can retain a large amount of liquid(e.g., over 1000 ml). The pads have been designed to reduce the numberof times that caregivers are required to change the pad while keepingthe patient dry. The absorbent middle layer quickly captures allmoisture and creates a dry interface with the patient. As a result, itmay be hard for a caregiver to accurately assess when the pad needs tobe changed.

A system that detects liquid in the absorbent layer of a pad in a mannerthat may be correlated to a volume of liquid, as discussed above, helpscaregivers to know when it is time to change a pad especially whenmanual inspection is difficult or inconclusive.

Incontinence conditions in long-term patient care include the followingfacts: the human bladder can hold between 1.5 and 2.0 liters of liquid;the average person urinates between 4 and 8 times per day and up to 20times per day if afflicted with an incontinence condition; a typicaldischarge of urine is between 150 ml and 240 ml; and a maximum dischargeof urine may be up to 700 ml.

When a patient is positioned over on a pad on a bed, the patient's bodyforms a depression in the pad and the bed. The depression in the padunder the patient tends to collect most of any discharged liquids.Because the discharged liquid is located under the patient, it is moredifficult for the caregiver to determine the status of the pad and whento change the pad. As the absorbent layer of the pad absorbs the liquid,the absorbent layer changes shape so that the surface of the pad againstthe patient is no longer substantially flat, but includes bumps (e.g.,lumps) so that the pad would likely apply uneven pressure on thepatient's body thereby increasing the likelihood that bedsores or skinirritations may develop. Once a pad is wet, the uneven surface of thepad may determine a maximum amount of time a patient may be on the padto reduce the probability of developing bed sores.

Testing provided information as to the spread of a volume of liquid in apad. Testing was performed using a product named the Peach model padproduced by Tranquility. The size of the Peach model pad is 76 cm by 91cm. It is a high absorbency pad that is rated to hold up to 1300 ml.Different amounts of liquid (e.g., 100 ml, 200 ml, 400 ml) were pouredslowing into the center of the Peach model pads to simulate dischargefrom a patient positioned on the pad. The testing showed the spread ofthe liquid in the pad for each amount of liquid.

Four hundred milliliters of liquid spread in the Peach model pad tocover an area having a diameter of about 36 cm. A rectangle draw aroundthe area of absorption was about 41 cm by 35 cm.

Two hundred milliliters of liquid spread in the Peach model pad to coveran area having a diameter of about 28 cm. A rectangle draw around thearea of absorption was about 32 cm by 25 cm.

One hundred milliliters of liquid spread in the Peach model pad to coveran area having a diameter of about 22 cm. A rectangle draw around thearea of absorption was about 25 cm by 22 cm.

When hand pressure was applied to the 400 ml and 200 ml test areas, thehand became moist to the touch. Moisture from these areas could betransferred to a patient's skin thereby resulting in skin irritation.When hand pressure was applied to the 100 ml test area, the handremained dry.

The spread of 400 ml of liquid covered a large portion of the Peachmodel pad and may result in the discomfort of the patient. The spread of100 ml of liquid covered only a small portion of the area of the Peachmodel pad. A caregiver likely would not want to change the pad after a100 ml discharge.

Further testing using the Peach model pad included pouring 200 ml ofliquid about 10 cm from the edge of the pad. In the Peach model pad, theabsorbent layer does not extend all the way to the edge of the pad. Thetop layer and the bottom layer of the pad extend about 2.5 cm beyond theedge of the absorbent layer and are bonded together. The 200 ml ofliquid was slowing poured onto the pad about 10 cm away from the edge ofthe pad and about 7.5 cm from the edge of the absorbent layer.

The 200 ml of liquid nearly immediately spread through the absorbentlayer and across the upper and lower layers to the edge of the pad andresulted in the liquid leaking from the pad. The testing showed thatliquid would leak from the pad even if a much smaller amount of liquidwere used. The testing further highlighted the desirability ofconductors that detect liquid at the boundary of an area to detectliquid that may leak from a pad.

A system for detecting a liquid in a hospital pad may be used to detectthe amount of liquid in the pad, the area where the liquid is positioned(e.g., center, edge), and whether liquid is exiting the pad. A systemthat detects liquid in a patient setting may further detect (e.g.,measure) the amount of time a patient has been on a wet pad.

In one implementation, a system for detecting liquid in a Peach modelpad establishes a boundary 3 cm from the edge of the absorbent materialin the pad, which is about 5.5 cm from the edge of the pad. As discussedabove, conductors of the system are positioned along the boundary sothat a circuit may be formed by liquid positioned along the boundary.Preferably the conductors along the boundary are positioned on theabsorbent layer so that the conductors are spaced at most up to 3 cmfrom each other. Because liquid at the edge of the absorbent layerspreads quickly past the edge of the pad to leak from the pad, oneconductor implementation positions a first conductor 3 cm from the edgeof the absorbent layer along the boundary and a second conductor at most2 cm away from the first conductor along the boundary.

Within the boundary of the Peach model pad, conductors are spaced atleast 25 cm from each other so that liquid must spread at least 25 cmbefore it forms a circuit between conductors. The spread of 25 cmrelates to between 100 ml and 200 ml of liquid in the pad when a circuitis formed between the conductors.

The conductor implementations discussed above may be used with the Peachmodel pad to detect liquid within a boundary and at a boundary of thePeach model pad.

The foregoing description discusses preferred embodiments of the presentinvention, which may be changed or modified without departing from thescope of the present invention as defined in the claims. Examples listedin parentheses may be used in the alternative or in any practicalcombination. As used in the specification and claims, the words‘comprising’, ‘including’, and ‘having’ introduce an open endedstatement of component structures and/or functions. In the specificationand claims, the words ‘a’ and ‘an’ are used as indefinite articlesmeaning ‘one or more’. While for the sake of clarity of description,several specific embodiments of the invention have been described, thescope of the invention is intended to be measured by the claims as setforth below.

What is claimed is:
 1. A pad for detecting a liquid, the pad comprising:an absorbent material, the absorbent material includes a perimeter alongan outer edge of the absorbent material; a first conductor, a secondconductor, and a third conductor; wherein: the first conductor, thesecond conductor, and the third conductor do not contact each other toform an electrical circuit between the conductors; the first conductoris positioned a first distance inside the perimeter along substantiallyan entire length of the perimeter; a first portion of the secondconductor and a first portion of the third conductor are positionedalong a length of a first portion of the first conductor and along alength of a second portion of the first conductor respectively, thelength of the first portion of the first conductor does not overlap thelength of the second portion of the first conductor; the first portionof the second conductor and the first portion of the third conductor arepositioned a second distance away from the first portion of the firstconductor and the second portion of the first conductor respectivelyalong a length of the first portion and a length of the second portionrespectively; a second portion of the second conductor is positioned athird distance from a second portion of the third conductor along alength of the second portion of the second conductor and a length of thesecond portion of the third conductor; a first electrical circuitbetween the first conductor and at least one of the second conductor andthe third conductor indicates that the liquid is positioned proximate tothe outer edge of the absorbent material so as to exit the absorbentmaterial; and a second electrical circuit between the second conductorand the third conductor indicates that the liquid is positioned withinthe perimeter.
 2. The pad of claim 1 wherein the second distance is lessthan the third distance.
 3. The pad of claim 1 wherein upon detectingthe first electrical circuit, a volume of liquid proximate to theperimeter is related to the second distance.
 4. The pad of claim 1wherein upon detecting the second electrical circuit, a volume of liquidwithin the perimeter is related to the third distance.
 5. The pad ofclaim 1 wherein the second distance is less than the third distancewherefore a first volume of liquid detectable proximate to the perimeteris less than a second volume of liquid detectable within the perimeter.6. The pad of claim 1 wherein prior to detecting a liquid proximate tothe perimeter, the liquid may spread a distance in a range of the seconddistance and about two times the second distance.
 7. The pad of claim 1wherein prior to detecting a liquid within the perimeter, the liquid mayspread a distance in a range of the third distance and about two timesthe third distance.
 8. The pad of claim 1 wherein: the first conductor,the second conductor, and the third conductor each contact a firstsurface the absorbent layer.
 9. The pad of claim 1 wherein the firstconductor, the second conductor, and the third conductor are eachpositioned at a same layer of the pad such that no conductor ispositioned above or below any other conductor.
 10. The pad of claim 1wherein a sum of the length of the first portion and the length of thesecond portion of the first conductor is substantially equal to a totallength of the first conductor.
 11. The pad of claim 1 wherein the firstconductor is positioned between the outer edge of the absorbent materialand substantially all of the second conductor and the third conductor.12. The pad of claim 1 wherein the first conductor is positioned betweenthe outer edge of the absorbent material and substantially all of thesecond conductor and the third conductor.
 13. The pad of claim 1 whereinthe first conductor, the second conductor, and the third conductor areformed as a first trace, a second trace, and a third trace respectivelyof conductive ink deposited on a first surface of the absorbentmaterial.
 14. The pad of claim 13 wherein the first trace, the secondtrace, and the third trace do not contact each other so as to form anelectrical circuit.
 15. A system for reporting a presence of a liquid,the system comprising: a pad, the pad includes an absorbent material, afirst conductor, a second conductor, and a third conductor; and areader, the reader for electrically coupling to the first conductor, thesecond conductor, and the third conductor; wherein: the absorbentmaterial includes a perimeter along an outer edge of the absorbentmaterial; the first conductor, the second conductor, and the thirdconductor do not contact each other to form an electrical circuitbetween the conductors; the first conductor is positioned a firstdistance inside the perimeter along substantially an entire length ofthe perimeter; a first portion of the second conductor and a firstportion of the third conductor are positioned along a length of a firstportion of the first conductor and along a length of a second portion ofthe first conductor respectively, the length of the first portion of thefirst conductor does not overlap the length of the second portion of thefirst conductor; the first portion of the second conductor and the firstportion of the third conductor are positioned a second distance awayfrom the first portion of the first conductor and the second portion ofthe first conductor respectively along a length of the first portion anda length of the second portion respectively; a second portion of thesecond conductor is positioned a third distance from a second portion ofthe third conductor along a length of the second portion of the secondconductor and a length of the second portion of the third conductor; thereader applies a first voltage across the first conductor and at leastone of the second conductor and the third conductor to detect a firstelectrical circuit between the first conductor and at least one of thesecond conductor and the third conductor; the reader applies a secondvoltage across the second conductor and the third conductor to detect asecond electrical circuit between the second conductor and the thirdconductor; responsive to detecting the first electrical circuit, thereader reports that the liquid is positioned proximate to the outer edgeof the absorbent material so as to exit the absorbent material; andresponsive to detecting the second electrical circuit, the readerreports that the liquid is positioned within the perimeter.
 16. The padof claim 15 wherein the first conductor, the second conductor, and thethird conductor are formed as a first trace, a second trace, and a thirdtrace respectively of conductive ink deposited on a first surface of theabsorbent material.
 17. The pad of claim 16 wherein the first trace, thesecond trace, and the third trace do not contact each other so as toform an electrical circuit.
 18. The pad of claim 15 further comprising afirst contact, a second contact, and third contact electrically coupledto the first conductor, the second conductor, and the third conductorrespectively; wherein: the reader mechanically couples to the firstcontact, the second contact, and the third contact respectively toelectrically couple to the first conductor, the second conductor, andthe third conductor respectively.
 19. The pad of claim 15 wherein thefirst conductor is positioned between the outer edge of the absorbentmaterial and substantially all of the second conductor and the thirdconductor.
 20. The pad of claim 15 wherein the first conductor ispositioned between the outer edge of the absorbent material andsubstantially all of the second conductor and the third conductor.